Surface area nanoporous carbons

As d is of the order of lnm, the specific capacity is very high, e.g., 0.1 F nr2. Nanoporous carbons are ideal materials for supercapacitor electrodes [8], because of their low cost, good electrical conductivity, and very high specific surface area (between 1000 and 2500 m2 g-1). The values of capacity are generally ranging from 100 to 200 F g 1. 

In the majority of cases nanoporous materials exist in a highly dispersed state (seldom - as films). It limits practical application of these materials and in many cases makes difficult for study of their properties. Samples of the nanoporous carbon (NPC) used in this work are produced as a body of cylinder shape with a sufficient mechanical strength. They synthesized by heat treatment of carbide silicon and carbide titanium in chlorine have been studied in the present work. The samples of materials are characterized by the advanced structure of pores, which contains two types of pores macropores (with the sizes in a few micron) and nanopores with sizes about 0.8 nm. Surface area and volume of pores NPC with... 

In these adsorbents an increase in carbon deposit content leads to reduction of the total pore volume, but an enhancement of the specific surface area (Sbet) and contribution of nanopores because the FDA value increases. A noticeable increase in nanoporosity of these carbosils is accompanied by significant changes in the pore size distributions (PSDs) at Rp < 2 nm (Figure 2). 

The synthesis of the CMK-n carbons is controlled to various pore shapes, connectivity, diameters (typically, 1-10 nm in diameter) and pore wall thickness. These carbons exhibit high specific surface areas (typically, the BET specific surface areas up to 2000 mV )> uniform pore diameters, large adsorption capacities, and high thermal, acid-base and mechanical stabilities. The CMK-type carbons are also suitable for the formation of well-defined nanocomposite with organic polymers, so that the nanopore walls can be modified with various functional groups. These carbons show new possibilities for various applications in adsorption, catalysis and electrochemistry. 

While oxidation is mainly used for purification of carbon nanostructures, it may also be an efficient tool for size control and surface modification. By selectively oxidizing, for example, smaller carbon nanotubes or diamond crystals, it can provide a simple technique for narrowing size distributions in carbon nanomaterials. Finally, modification of the porosity (activation) of carbon is another example of controlled oxidation and may allow optimization of the pore structure and surface area of nanoporous carbide-derived carbon (CDC) for various applications. 

Carbon (C)-aerogels have been investigated for one decade as a promising material for electrochemical applications in supercapacitors, fuel cells and waste water treatment [1,2], C-aerogels are nanoporous, electrically conducting and monolithic materials that provide the unique possibility to tailor the carbon properties on a molecular scale. The surface area and the degree of microporosity can be adjusted almost independently of the overall porosity for which mainly meso- and macropores are responsible. Whereas the mesostructure is determined by the stoichiometry of the reactants in the precursor solution, the pyrolysis conditions control the micropore structure of the material [3,4]. High pyrolysis temperatures will increase the electrical conduchvity [5], an important property for many electrochemical applications. 

To avoid high-pressure drop and clogging problems in randomly packed micro-structured reactors, multichannel reactors with catalytically active walls were proposed. The main problem is how to deposit a uniform catalyst layer in the microchannels. The thickness and porosity of the catalyst layer should also be enough to guarantee an adequate surface area. It is also possible to use methods of in situ growth of an oxide layer (e.g., by anodic oxidation of a metal substrate [169]) to form a washcoat of sufficient thickness to deposit an active component (metal particles). Suzuki et al. [170] have used this method to prepare Pt supported on nanoporous alumina obtained by anodic oxidation and integrate it into a microcatalytic combustor. Zeolite-coated microchannel reactors could be also prepared and they demonstrate higher productivity per mass of catalyst than conventional packed beds [171]. Also, a MSR where the microchannels are coated by a carbon layer, could be prepared [172]. 

Platinum nanoparticles/ nanoporous carbons composites have been synthesized from mixtures of Pt complex salts, surfactants and a resorcinol-formaldehyde (RE) resin. The composite has high BET surface area and large micropore and mesopore volume because of gas generation from surfactant molecules. The product has well-dispersed small Pt particles with a diameter of... 

Ordered mesoporous carbons (OMC) of various structures, designated as CMK-1 5, have been synthesized by carbonization of sucrose, furfuryl alcohol or other carbon sources inside silica or aluminosilicate mesopores that are interconnected into three-dimensional networks such as in MCM-48, SBA-1 and SBA-15. The mesoporous carbon molecular sieves, obtained after template removal, show TEM images and patterns characteristic of the ordered arrangement of uniform mesopores. The OMC, which are opening up a new area of the nanoporous materials, exhibit high BET specific surface areas, excellent thermal stability in inert atmospheres and strong resistance to attack by acids and bases. 

Carbonaceous materials such as porous carbons (e.g., active carbons and ordered nanoporous carbons) and nonporous carbons (e.g., carbon blacks) are a non-graphitic form of carbon characterized by internal surface areas ranging from lO-AO m g (nonporous or macroporous carbon blacks) to 500-3000 g" (active carbons). X-ray analysis shows that... 

Gas adsorption is an important method for characterization of nanoporous carbons because it allows for evaluation of the specific surface area, pore volume, pore size, pore size distribution and surface properties of these materials [1, 10-12]. Although various techniques for measurement of gas adsorption data and methods of their analysis pear to be well established, an accurate and reliable evaluation of adsorption properties is still a difficult task. This can be attributed to the inherent features of many porous carbonaceous materials, namely, to their strong surface and structural heterogeneity. The effects of structural and surface heterogeneity in adsorption on nanoporous carbons are often difficult to separate. 

The Os-plot method provictei an effective and simple way for evaluation of the micropore volume the total surface area S, and the mesopore surfece aura of nanoporous materials. For the purpose of illustraticm. Fig. 8 presents the Os-plot for the nitrogen adsorption isotherms on seladed active (srbcsis at 77 K. The values of Si and S,m evaluated from nitrogen adsorption data for the WV-A900, BAX 1500 and NP-5 active carbons are summarized in Table 4. 

Industrial applications of nanoporous carbons are based on both their porosity and surface properties, and consequently, their characterization is of great importance. The results presented here demonsfrate a great usefulness of gas adsorption measurements for the characterization of nanoporous carbons. Low-pressure measurements provide an opportunity to study the microporous structure and surface proptaties of these materials and to monitor changes in these properties that result fiom structure and surface modification. High-pressure adsorption data allow for a detailed characterization of mesoporous structures of carbonaceous porous materials, providing their surface areas and pore size distributions. 

The catalytic formation of carbon nanotubes on Fe-loaded zeoHte supports with different pore sizes has been investigated [70]. Mossbauer spectroscopy showed that the Fe(II) species seemed to catalyse the formation of the carbon nanotubes. Mossbauer spectroscopy has been used to study the electronic state of iodine adsorbed in nanoporous graphite fibres with very high surface areas. The observed spectra consisted of five Afferent quadrupole octets demonstrating the coexistence of I3 and I2 molecules in the pores this indicates that charge transfer from the graphite to the iodine had occurred [70]. 

The third group, Styrosorb 2, represents nanoporous single-phase polymers derived from spherical beads of gel-type styrene copolymers with largely 0.7% DVB, post-crosslinked in swollen state with monochlorodimethyl ether. The size of the micropores is approximately 10—30 A, and the apparent specific surface area reaches very large values of 1000—1900 m /g, which is comparable to the range of the best activated carbons. On the other hand, the pore volume of these materials is rather small, 0.2—0.3 cm /g. 

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